Oil prices jumped by nearly 7% after US President Donald Trump reiterated threats to hit Iran "extremely hard" in the coming weeks and failed to give concrete details on how the war will end.

Brent crude rose to $107.60 a barrel and stock markets in Asia fell following Trump's address from the White House.

He said that the US would complete its strategic objectives for the war "very shortly" and spend the next two to three weeks bombing Iran "back to the Stone Ages".

Earlier on Wednesday, oil prices briefly dipped below $100 ahead of the speech on hopes Trump would say how the US would exit the conflict but his address repeated the same points he made previously.

The Iran war has severely disrupted global oil and gas supplies.

Oil shipments through the critical Strait of Hormuz waterway have mostly halted after Iran threatened to attack tankers that try to cross in retaliation to US-Israeli strikes, which began on 28 February.

In his speech, Trump said the US does not need Middle East's energy and urged other nations to step in to free up shipments from Gulf that have been disrupted as a result of the war.

He said: "To those countries that can't get fuel, many of which refuse to get involved in the decapitation of Iran… build up some delayed courage, go to the Strait and just take it."

Oil prices, which had been fluctuating incrementally before, shot upwards moments after the televised speech.

West Texas Intermediate oil rose 6.4% to about $106.50.

The gains are a "clear market reality check following the earlier optimism for an imminent ceasefire" said Alberto Bellorin from InterCapital Energy.

Trump's speech lacked a "concrete timeline" for the reopening of the Strait of Hormuz, while a return to normal now looks "months away rather than weeks," he added.

In urging other nations to step in, Trump has removed hopes that disruptions to global energy supplies will be resolved swiftly, Bellorin said.

Trump has signalled that the war is likely to continue, prompting investors to expect that oil supplies will remain tight, said Tina Soliman-Hunter from Macquarie University.

Major stock indexes in Asia fell after the address, reversing earlier gains.

The Nikkei 225 in Japan was down by 2.4%, South Korea's Kospi fell by 4.5% and the Hang Seng in Hong Kong was 1.3% lower.

The region's stock markets have been volatile since the Iran war started at the end of February.

Asia is particularly vulnerable to the impact of the conflict as it is heavily reliant on the Middle East for its energy supplies.